The molding process is comprised of four process elements that the molding technician has control of.
If you change one you will change them all. and on top of this by the time he receives the mold all the problems he will encounter are designed into it , so his challenge is to find a process to overcome the design errors. In addition the material has variation and the press does not always repeat and then the quality department may have some subjective aesthetic requirement that must be interpreted on a constant basis. If that is not bad enough then you have molding and quality technicians from each shift that can that add their own spin on how to mold the product better using their process.